Circuit Wiring Joint boxes, Consumer Electronics Home Guide

Joint boxes are usually circular and for part of the circuit wiring. They are fix permanently to the house structure are used principally in lighting circuits. Join boxes are available in 4- 5- and 6-terminal versions.

A 3-terminal joint box of 30 A current rating is used for ring circuits to connect spur cables to the ring cable, as shown the illustration.

Socket-outlets

The socket-outlet is the fixed portion of a plug and socket arrangement and the termination point of circuit wiring to provide a ready means of connecting portable appliances to the fixed mains wiring.

The 13 A socket-outlet for use with the flat-pin fused plug is the standard socket in Britain for domestic installations. It is made in many variants: single switched socket, single non-switched socket; double socket, switched and non-switched, and switched with neon indicator. All these versions are available in the plate type for mounting on surface and flush boxes.

The single socket is mounted on a 1-gang box; the double on a 2-gang box, and two singles may be mounted side by side on a dual box. This dual box is slightly wider than the double or 2-gang box and has extra screw lugs for the separate sockets.

Surface pattern socket-outlets are designed only for surface mounting and are usually mounted on a pattress.

Fused round pin plugs

Although the fused plug is associated with the 13 A flat pin plug and socket of the ring circuit, fused round pin plugs are made to the appropriate British Standard (BS 546) and may be found in some homes. The fuses are of the cartridge type but slightly smaller than the 13 A plug fuse. The ratings and colours are: 5 A (red); 2 A (yellow) and 1 A (green), made to BS 646.

These fuses are fitted in some clock connectors, so if the clock connector has either a 2 A or a 1 A fuse, check whether it is stamped BS 642. If it is, buy the same size replacements and not a 2 A (black) or 3 A (red) which are for 13 A plugs.

Fused connection units

A fused connection unit (originally known as a fused spur box) provides a fused outlet in a ring circuit as an alternative to a fused plug and socket-outlet. It is used to supply fixed appliances and remotely positioned fixed lighting.

The fuses are cartridge fuses of the same size, colours and current ratings as used with the 13 A fused plug.

Proposed 16 A plug

An entirely new plug and socket outlet having a current rating of 16 A is being developed world-wide and will replace all existing plugs and sockets including the 13 A fused plug and the round pin plugs used in the UK. It is unlikely to be in production before 1980 and it will be many years after this before existing plugs and sockets are entirely obsolete.

It is also expected that the 13 A ring circuit sockets will be able to be replaced without modification to existing wiring.

The sockets will probably be twin units for mounting on a one-gang box, but for the ring circuit the twin unit will consist of one socket and a fused unit.

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